From Go! Comi:

On the distant planet of Deloca, teenagers enroll in an education system like no other – a mobile journey that takes place onboard a train. There are standard School Trains for general studies...and then there's the Special Train, an expectional institution whose students receive anything but a normal education. Reiichi is a student contented to obediently follow the tracks laid out before him…but when Arena, a rebellious girl with a mysterious past, enters the scene, his life is completely derailed! While dodging the persistent investigator after Arena, Reiichi and his unintended partner-in-crime experience a school year never to be forgotten.